1. Field of the Invention
Generally the invention relates to forming milled depressions in an asphalt road surface. More specifically the invention relates to forming shallow depressions in a milling through operation by propelling a cutting head forward while in contact with the asphalt surface while regulating a lowering and raising motion.
2. Description of the Prior Art
Sonic noise alert pattern, (SNAP), are a series of shallow depressions formed in the surface of asphalt roads. The pattern has the purpose of providing vibration and noise when the tires of a vehicle traverse them longitudinally. Road departments use these depressions as a safety device. Longitudinally adjacent the edge of a highway or along the center line which divides the opposing directional traffic flows are common locations of placement. They act to alert a driver that his or her vehicle has extended beyond the normal driving surface. Beyond this normal driving surface many dangerous conditions exist for a vehicle traveling near the posted speed limit. These dangers include, amongst others, dirt or gravel shoulders, guardrail barriers, signs, mailboxes, intersecting roadways or driveways and stationary vehicles. Limited access highways and rural roads are likely locations for SNAP depressions to be installed due to the fatigue that a driver experiences during extended driving on such roads.
The various specifications for the physical dimensions of the individual depressions and their respective placement can vary from state to state and even within a particular state. A common size and placement, used only for illustration and not limitation, places the individual depressions twelve inches apart from center of one depression to center of each adjacent depressions. The measurements of the individual depressions being seven inches from back trailing edge to front leading edge with a depth, at the deepest point, of one half inch and a lateral length across of sixteen inches. These specifications result in five inches of uncut surface between each set of adjacent depressions. Therefore, the above specifications would require fifty-two hundred and eighty cuts per mile.
A recent innovation in the specifications for the installation of SNAP type depressions requires a skip pattern to be incorporated within the series. One example of such a series has eight depressions spaced as detailed above followed by an uncut area equal to the normal placement of four depressions. Such installation affords reasonable coverage of a highway while reducing installation expense. Limited access highways and rural roads are likely locations for SNAP depressions to be installed due to the fatigue that a driver experiences during extended driving on such roads.
Conventional installation of SNAP type depressions utilize at least one rotary cutting head with a plunge cut from a stationary position. Following the stationary plunge cut the machine is advanced, paused and the cutting procedure repeated. This action is repeated in a repetitive manner along the desired path of the series.
Various attempts have been made to provide a machine capable of quickly, accurately, consistently and precisely installing SNAP type depressions. These attempts have been less efficient than desired. As such, it may be appreciated that there continues to be a need for a method of forming SNAP type depressions using a milling through operation. And for a method which can consistently form depressions in a continuous, non pausing, manner having precise placement and precise dimensions. The present invention substantially fulfills these needs.